Re: phase comparator

From: Jamie Morken (jmorken_at_shaw.ca)
Date: 01/04/05 

Date: Tue, 04 Jan 2005 20:27:09 GMT

Hi,

I think I see now that if the two input signals have different
frequencies then the output of the phase comparator will cycle at the
beat frequency of the two input signals.

cheers,
Jamie

Tim Wescott wrote:
> Jamie Morken wrote:
>
>> Hi,
>>
>> I would like to compare the phase of two 1MHz sinewave and/or
>> squarewave) signals and get a output voltage proportional to their
>> phase shift, with a small phase angle error ie. 1% if possible. Also
>> what happens when the amplitudes of the two input signals are
>> different, and what happens if the frequency isn't exactly the same?
>> (ie. from a doppler shift)
>
>
> This can be done, various phase detectors will handle the level issue
> differently.
>
>>
>> Is there a common circuit for comparing the frequencies of two signals
>> as well (and outputting a voltage proportional to the frequency
>
>
> Discriminator, as used in FM radio. However, a three-state
> phase/frequency detector with an appropriate loop filter will often do
> well enough without a bunch of fussy resonant circuits.
>
>>
>> Is an XOR gate with a lowpass filter on its output essentially a phase
>> comparator?
>
>
> Yes, as is a double-balanced mixer.
>
>>
>> I am slowly learning more about modulators/demodulators and
>> upconverters and downconverters, and am a bit confused on how these
>> devices can be used for FM and PSK etc..
>>
>> Is there a reason why an IQ modulator/demodulator can be made to
>> operate over a large frequency range without needing external tuning
>> caps/coils (ie. AD8346/AD8347) while a downconverter/upconverter (ie.
>> max2680/max2660) requires external tuning passives depending on the
>> frequencies of operation? Is this because an IQ modulator/demodulator
>> is "balanced" from the I and Q being 90degrees out of phase?
>
>
> There's no fundamental reason -- a downconverter that's going to a
> non-zero IF ("image reject") may need better phase matching, but it's
> probably mostly the manufacturers.
>
>>
>> cheers,
>> Jamie Morken
>
>
> "Phase Lock Loop Circuit Design" by Dan Wolaver is a good book. Not a
> classic, but I think it could be if it caught on. It seems to be pretty
> clear for self study (but I wouldn't know -- I took the class from Dr.
> Wolaver).
>